1. Field of the Invention
The field of the present invention is that of the surface treatment of mechanical components and, in particular, that of the compaction of anodic paints for protecting turbo machine components.
2. Description of the Related Art
Certain aircraft engine components are very heavily mechanically loaded and only special-purpose materials are able to meet the mechanical integrity requirements imposed upon them. These materials in general have the disadvantage of being very sensitive to corrosion; it is therefore absolutely essential to protect them with a product capable of withstanding the environment in which these components move (high temperature, presence of engine oil, kerosene, etc. . . . ). The anticorrosion protection currently used involves covering the component with a paint that is resistant to high temperatures and to the aforementioned various fluids. However, because this paint is classified as CMR (carcinogenic, mutagenic, reprotoxic), it is hit by the REACH regulations regarding the registration, evaluation, authorization and restriction of chemicals. It has therefore become necessary to look for a new method of protection in order to get around the constraints associated with these regulations.
A first solution is to base the protective system not on the mere principle of covering with a paint but on a physicochemical process referred to as anodic paint. This process consists in spraying onto the surface of the component a liquid which is laden with metallic pigments, such as aluminum or zinc pigments, then in heating the component in a furnace to polymerize the sprayed product. This results in a tough protective layer which protects against oxidation as long as it is not scorched, but which has the property of not being conducting. As soon as the component becomes scratched or scorched, the protection ceases, the component becoming sensitive to electrochemical corrosion. In order to guard against this risk, the surface layer needs to be made conductive in order to create a sacrificial layer which will corrode for preference, in place of the metal of the component that is to be protected.
The expression anodic paint is then used to denote the superficial layer thus rendered conducting. In order to achieve that, the metallic particles incorporated into the formulation of the paint need to be orientated through a mechanical action after polymerization, without impairing the cosmetic appearance thereof. There are two methods commonly used to that end:
burnishing, which involves rubbing the painted parts after polymerization in the same direction, using a metallic sponge. This action makes it possible to achieve electrical continuity on the treated parts. By contrast, this is a manual action which is difficult to automate and cannot therefore be employed on an industrial scale, and one in which there is a not-insignificant risk that component regions that are difficult to access will not be treated.
compaction, which involves sand-blasting the painted parts after polymerization. This action makes it possible to achieve electrical continuity on the treated parts. However, it has to be performed at very low pressure in order not to impair the treated zones. By contrast, in order to keep the sand-blasting installation operating correctly, it needs to maintain a relatively high service pressure and, in any case, a service pressure that is too high for treating the component; in the current state of affairs, that results in the quality of the coating obtained being systematically impaired.
It is therefore necessary to find a method that allows the compaction of anodic paints using sand-blasting that respects the quality of the coating of the treated components.